Antenna switching system



C. A. ROSENCRANS ANTENNA SWITCHING SYSTEM April 17, 1951 Filed June 23, 1945 Y PULSE Ol? MODULATED SOURCE lllllll fllllllll II rmx/.6.

. INVENTOR. [albfenawzi Patented Apr. 1'7, 1951 UNITED STATES PATENT GFFICE ANTENNA SWITCHING SYSTEM Charles A. Rosencrans, Haddoneld, N. J., assignor to Radio Corporation of America, a corporation of Delaware ApplicationI June 23, 1945, SerialfNo. 601,127

2 Claims. (Cl. Z50-13) I and 23. A pair of smaller discs 25 and 21 may'v provide separate antennas for transmission and reception. In order to prevent damage to the receiver during transmission, and useless dissipation of power, it is necessary to provide means for `electrically isolating the receiver from the transmitter.

` It is the principal object of the instant invention to provide* ,an improved method of and means for isolating the receiver from the transmitter in systems of the described type.

The invention will be described with reference tothe accompanying drawing, of which Figure 1 is a' schematic diagram of a pulse radio system embodying the invention, and

Figure '2 shows amodification of Figure 1. Similar reference charac-ters yare applied to ksimilar elements in the drawings.

Various systems exist for isolating the receiver from` the' transmitter toenableuse of a common` antenna. A typical prior art system involves one or more spark gaps, glow tubes, or other discharge devices arranged to break down (i. e. conduct) in response to output from the transmitter. The change in impedance of the discharge device effects transfer of the antenna connection from' the receiver to the transmitter.

In accordance with the present invention, the necessary switching is not provided in response to the transmitter output, but is effected by means of a control voltage, which may loe-conveniently obtained front the modulation input to the transmitter.

Referring to the drawing, a radio transmitter.

I is connected through a transmission line 3 to an antenna 5. The transmitter I includes a modulation input circuit, which is connected to a has a length of substantially one. quarter Wavelength, or an odd integral multiple thereof.

y The line S-termina-tes in aresonator I3 which in the present illustration comprises a cylindrical outer conductor I5 and: a pair of coaxial inner 2. conductors IT and I9, connected to the respective ends of' the outer conductor I5 byV discs 2t be provided at the adjacent innerk ends/of' the l inner conductors T and I9.

vThe inner conductor of the line 9 extends into the resonatorv t3 in a loop 29 to a pointv 3l on the outer conductor I5.V The loop29 provides coupling to the innery conductor' I9 fromthe line 5.

A detector 34', lsuch asa crystal or other coritact rectier, isv connected to a point. 3l' on the inner conductor IT and to a load 35 passing through a hole in the outer conductor I5. The lead 35 extends to an amplifier and an indicator' 4D', 42, one' ofv which is connected to a contact dSC 01" plug IH' in the inner conductor I'I. The" other electrode 4?; of the' tube 39' is 'connected' I through a wire 43 to the pulse source 7.

In the operation of' the described system, the resonator I3 acts like a lo`w-lossparal'lel'- reso'-,

tion as a shunt capacitor, and their principal' eilectv is to lower the resonance frequency, so.. that the resonator structure may be made smaller, for a given' frequency than it would be if they were omitted'. l

Theimpedance presented' to the line 9 bythe loop 25 iskalso resonant owing to'v coupling tothe resonatoigbut' is relativelyl'ow and may be approximately equal' to the surge impedance of the" al small shunt capacitance across the resonator. Signals,A picked up byl the antenna 5 are con-f" ducted-through the lines 3 and 9K' tok the resonator" e; Y J 31, vhich functions as a sharply tuned auto transformer to transfer the energy to the detector 34. A portion of the received energy goes to the transmitter I. This may be minimized if necessary by proper design of the transmitter output circuit.

With each pulse in the output of the pulse source 1, the transmitter I provides a corresponding pulse of radio frequency energy, which is conducted to the antenna through the line 3. Simultaneously the pulse voltage is applied to the tube 39 through the connection 43, causing the tube 39 to become conductive.

The upper electrode of the tube 39 is connected to the conductor I1 by the plate 4I. The lower electrode is effectively connected to the conductor I9, insofar as the radio frequency energy is concerned, by virtue of concentric line action between the wire 43 and the conductor I9. The open circuit between these two members at the lower end of the conductor I9 is reflected as a short circuit between the upper ends of the Wire 43 and the conductor I9.

The impedance of the tube 39 when conductive is so much less than that of the resonator I3 that it acts substantially as a short circuit across the resonator, Also the dielectric constant of the gas in the tube 39 changes with ionization, detuning the resonator to some extent. The impedance presented by the loop 29 to the line 9 is accordingly substantially Zero. Since the line 9 is a quarter wavelength long, the short circuit at the one end is reflected as `an open circuit at the other end. Thus the line 9 presents a substantially infinite impedance at the point Il, and practically none of the output of the transmitter can now into the receiver. At the end of each transmitted pulse, the gas in the tube 39 deionizes substantially instantaneously, restoring the system to the receiving condition.

Although a specific embodiment of the invention has been described it is to be understood that the practice of the invention is not restricted thereto, but may be carried out with other apparatus. For example, telegraphic code or voice modulation may be employed instead of pulses. The specific resonator structure shown in Figure 1 may be modified, as shown in Figure 2 by way of example.

Referring to Figure 2, the resonator I3 may be replaced by a quarter Wavelength coaxial line comprising an outer conductor 5l and an inner conductor 53, connected together at their lower ends by a disc 55. The inner conductor 53 is tubular, and encloses a coaxially disposed conductor 51, which is connected through a wire 43 to the modulation source, not shown. The upper end of the conductor 51 is connected to one electrode of a glow tube 59. The other electrode of the tube 59 is connected to a disc 5I closing the upper end of the outer conductor 5I.

A line 9 extends from the resonator to the antenna system, as in the system of Figure 1 and is coupled to the resonator by a loop 29. A point 31 on the inner conductor 53 is connected through a line 63 to a detector, not shown in Figure 2.

The system of Figure 2 operates in substantially the same manner as that of Figure l. The inner conductor 53 cooperates with the innermost conductor 51 to act as a quarter wavelength coaxial line, presenting a shirt circuit for radio frequency energy at its upper end, thus ef- 4 fectively connecting the lower electrode of the tube 59 to the upper end of the conductor 53.

When the tube 59 is non-conductive, the resonator acts like a transformer between the lines 9 and 63. When the tube 59 is conductive, the resonator presents a short circuit across the line 9.

Thus the invention has been described as an improved method of and means for isolating a receiver from a transmitter connected to a common antenna. This is accomplished by means of a voltage responsive switching device connected between the antenna and the receiver, comprising a resonator and a discharge tube energized by the modulation input to the transmitter. I claim as my invention:

l. In a radio system including a transmitter, a pulse generator including output terminals connected to said transmitter to modulate the output thereof, an antenna, a transmission line connected from said transmitter to said antenna, and a detector: switching means including a cavity resonator coupled to said detector and having as a wall portion thereof a hollow conductor which terminates within said resonator, a leadin conductor within and insulated from said hollow conductor and forming therewith a second transmission line having an odd number of quarter wavelengths at the operating frequency open circuited at the other termination of said hollow conductor, a third transmission line an odd number of quarter wavelengths long connected from said resonator to said rst transmission line, and voltage responsive discharge means within said resonator and including two electrodes connected respectively to said hollow conductor and said lead-in conductor, said hollow and lead-in conductors being connected to said output terminals of said pulse generator, whereby pulses from the pulse generator may be applied to said electrodes and radio frequency energy at the operating frequency is inhibited from escaping said resonator.

2. A switch device for radio frequency energy, including a cavity resonator comprising an outer conductor, a hollow tubular inner conductor enclosed by said outer conductor and connected at at least one of its ends to said outer conductor, said inner conductor including a longitudinal gap, a voltage responsive gas discharge device including two electrodes positioned at opposite sidesoof said gap, and a further conductor extending within said tubular conductor and insulated therefrom and connected to one of said electrodes said other electrode being coupled to said cavity resonator outer conductor; coupling means for applying radio frequency power to said resonator; coupling means for absorbing radio frequency'power from said resonator, and means for applying a keying voltage between said further conductor and said outer conductor to make said discharge device conductive and effectively short circuit said gap and .thereby prevent the transfer of power from one of said coupling means through said resonator to the other of said coupling means, said hollow inner conductor from said gap to said connection to said outer conductor forming with said further conductor a transmission line having an odd number of quarter wavelengths at the operating radio frequency and open-circuited at said one end,

thereby to inhibit the escape of radio frequency energy from said resonator at said gap through said hollow inner conductor at said operating f I frequency.

CHARLES A. ROSENCRANS.

REFERENCES CITED f The following references are of record in the le of this patent:

UNTED STATES PATENTS Number Name Date Girardeau Aug. 20, 1912 Number Name Date Brown Aug. 16, 1932 Hoffman June 25, 1946 Richmond July 2, 1946 Richmond July 2, 1946 Evans Nov. 5, 1946 Patterson Dec. 3, 1946 Brown Dec. 10, 1946 Rochester Dec. 17, 1946 Kirchner Dec. 9, 1947 Barrow et a1 Nov. 30, 1948 

